Babies of smokers have levels of the nicotine byproduct cotinine in their urine that are five times higher than babies of non-smokers, researchers report.

Cotinine may harm the heart and blood vessels by boosting both blood pressure and pulse, Dr. M. P. Wailoo, of the University of Leicester, United Kingdom, who was involved in the research, told Reuters Health.

Cotinine is just one of a number of potentially harmful compounds found in tobacco smoke. Passive smoking exposes babies to cotinine at an early stage of life when they may not be fully equipped to excrete the toxic chemical.

Wailoo and colleagues measured the amount of cotinine in the urine of 71 infants with smoking parents and 33 infants with non-smoking parents when the infants were just 10 to 12 weeks old.

On average, cotinine levels were 5.58 times higher in infants who had at least one smoking parent compared with infants whose parents did not smoke, the researchers report in the Archives of Disease in Childhood.

Having a mother who smoked was the single largest contributing factor, the investigators report, increasing cotinine levels by a factor of four. By contrast, having a father who smoked increased cotinine levels by a factor of two.

The researchers also found that babies who slept in the same bed with a smoking parent tended to have higher cotinine levels. Furthermore, cotinine levels were generally higher during colder weather when parents may be more likely to smoke indoors.

These findings, the investigators say, indicate that babies become heavy passive smokers when their parents smoke.

SOURCE: Archives of Disease in Childhood, November 2007.